update README.md to mention logpath, add some links, and remove mention of descr files
update README.md to mention logpath, add some links, and remove mention of descr files

mattam82/coq-opam-archive,mattam82/coq-opam-archive,gmalecha/opam-coq-archive,mattam82/coq-opam-archive,coq/opam-coq-archive,gmalecha/opam-coq-archive,gmalecha/opam-coq-archive